Acoustic signaling device



Aug. 11, 1936.

J. F. MORAN ACOUSTIC SIGNALING DEVICE Filed Fab. 3, 19:52 2' sums-sheet1 INVENTOR John/171cm WWW 2 She ets-Sheet 2 J. F. MORAN" ACOUSTICSIGNALING DEVICE Filed Feb. 5, 1952 Aug. 11, 1936.

INVENTOR fir/an I'Moran ATTORNEY Patented Aug. 11, 1936 UNITE STATESPATENT OFFICE soousrro SIGNALING osvica John I. Moran, Jersey City, N.1.

Application February 3, 193:, Serial No. 590,513

' 10 Claims. (01. 111-1)- My present invention is shown as embodied in aso-called horn of the type commonly employed on automobiles, as warningsignals. It relates more particularly to the horns of the type in whichthe signal waves are generated by an elastic diaphragm which is actuatedby fluctuating or intermittent attraction of an electromagnet, Thediaphragm is permitted to swing freely on both sides of normal, and theelectromagnetic retractment to synchronize the energizing current andresulting electromagnetic attraction to the frequency of that diaphragm.

In certain cases, an interrupter is employed which is independentlytuned to the frequency of the diaphragm, in which case, anything varyingthe natural frequency of the diaphragm or the tune of the interrupterwill put the electromag-v netic pulls and the diaphragm out of step. Inother cases, the diaphragm itself is used as a driving mechanism toactuate the interrupter. but this involves mechanical connection withthe diaphragm which interferes with its free swing and to that extentchanges its natural frequency and otherwise interferes with itsfunctioning as a free elastic vibrator.

As concerns this aspect of my invention, it contemplates anelectromagnet and control mechanism in the horn casing behind the maindiaphragm which is practically aperiodic as concerns all frequencieswhich are, desirable for horns of this type. The desirable frequenciesare within the range, 350 to 750 complete vibrations per second, and themost desirable range is much narrower than this. Important points arethat such aperiodic mechanism is controlled by the diaphragm withoutpreventing its free swing or" swings of the diaphragm. Variousstructurally novel features each involving functional novelty,

may be employed in partial or complete combination, according to thedegree of emciency and per- 'fectionoffunctioningthatmsybereduiredin anygiven instance.

In the preferred form, the novel features include contributing factorsas follows:

The electromagnet is of course located within the horn casing, inopposite relation to a suitable armature on the rear face of the frontdiaphragm. Within the casing is asecond diaphragm having one faceexposed to the air pressures within the casing, so related to or remotefrom, the main diaphragm that it does not constitute a substantial loadtending to limit the amplitudes of swing of the main diaphragm. Theopposite face or this 5 supplemental diaphragm is preferably exposed toatmospheric pressure so that internal pressures will be operative toforce movements of the supplemental diaphragm. The preferred location ofthe supplemental diaphragm is in the rear of the electromagnet,preferably coaxial and'parallel with the front diaphragm.

An important feature of the supplemental diaphragm is to suppress itsnatural frequency of free vibration, and this is accomplished first, bylimiting its possible movement under air pressure. substantially to andfrom one side of normal, so that it cannot build up any resonantvibration in its own frequency; second, selecting a diaphragm of highnatural frequency as compared with the front diaphragm, so that itselastic return to normal after it has been displaced by internal airpressure will be substantially faster than the varying internalpressures which caused its displacement and its return.

Another important feature of the invention concerns avoiding the effectsof resonance in the air column that transmits the pressure changes fromthe rear face of the sound generating diaphragm to the front face of thesound actuated 40 diaphragm. I have discovered that where the operatingelectromagnet is located between said diaphragms as in my construction,and where the distance between the diaphragms is substantlally-less thanthe quarter wave length of the sound wave produced by the frontdiaphragm,

the air column may be made to actuate the rear diaphragm in properphase, without utilizing the cumulative efl'ects of air column resonancewhich have been relied upon in certain prior art devices. For instance,in my device, if the distance between the front and rear diaphragms is2% inches (which would be a quarter wave length for 1200 frequency).diaphragms having, any of the fundamental frequencies desirable for an55 automobile horn, say, 400 to 750 complete bodily swings per second,may be use interchangeably. This proves that the air column functions asa substantially aperiodic medium; and the device does not have to bedesigned with reference to the frequency of the signal wave produced bythe swing of the diaphragm. It will be evident that even in such cases,there will be a substantial time lag between rearward pressure exertedby the front diaphragm and the taking eifect of said wave upon the reardiaphragm, but this is desirable because, as explained below, thepressure on the rear diaphragm is utilized to decrease the energizingcurrent in the electromagnet; and it is desirable that this should notbe greatly decreased until after the diaphragm has completed its rearswing.

The rear diaphragm having only forced movement rearward from normal andelastic return terminating at normal, is utilized to control the currentin the electromagnet, preferably by varying the pressure on theelectrode of a microphone ,in series with the current, although incertain cases, make and break contacts may be substituted for themicrophone. The microphone is particularly desirable because sparking isentirely avoided and no deterioration can occur within the microphone;also the microphone is eflective for varying the current in theelectromagnet in response to mere variations of pressures of the reardiaphragm against the electrodes, even where the decrease of pressure isinsufficient to substantially move the center of the diaphragm, thusproviding initial weak current variations required to build up the swingof the main diaphragm to the point where the internal pressures willcause positive wide movements of the rear diaphragm, as in full normaloperation. The make and break can be employed so as to produce somewhatsimilar effects by minute arcing between the contacts, with or withoutcomplete make and break.

Between the rear diaphragm and the movable element of the microphone orother current varying mechanism, is a link operating as a thrust membernormally tensioning the rear diaphragm rearwardly and pressing themovable element of the microphone or other current varying mechanismforwardly; but when pressure on the rear diaphragm forces it rearwardly,the link operates as a tension member to positively retract the movablemember of the current varying meche anism. While satisfactory operationmay be achieved by rigid coupling, the efficiency of operation may begreatly increased by interposing a lost motion connection, affordingpredetermined intervals between thrusts and retractions, and during suchintervals the air pressures in casing act on the microphone diaphragm todelay releases and reapplications of pressure on the current varyingelement. The link is preferably adjustable in length so that the initialflexing of the rear diaphragm may be properly predetermined.

The lost motion connection may be either elastic, as where a felt orsimilar elastic washer is employed; or it may be a complete non-elasticlost motion as by providing a definite degree of longitudinal playwithin the coupling, as for instance, by having a screw element of themicrophone connection formed with threads a predetermined amount smallerthan the thread of the diaphragm member of the coupling.

The electromagnet is preferably of the ironclad, central-pole type andits axial length is preferably as small or smaller than its diameter,thereby minimizing the permissible distance between the front and reardiaphragms without sacrifice of electromagnetic efficiency. In thisconnection, it is to be noted that the electromagnet may fill upapproximately half or more than half the cross-section of the casing,leaving only a relatively narrow air space for front to reartransmission of air waves or pressures from the front diaphragm to therear diaphragm. It will be further noted that the air space between therear of the magnet and the rear diaphragm is substantial, so that this,taken with the annulus, constitutes an irregular cup-shape, relativelyobstructed cavity, which acoustically considered, is very far fromdeveloping any clear resonance such as the casing itself would be if itwere empty. This is a factor contributing to aperiodicresponse qualityof the elastic air medium whereby rearward pressure of the frontdiaphragm is transmitted to the rear diaphragm. The annular spacebetween the magnet; and the casing is obstructed by supports and may berelatively small cross-section so as 0 have a damping and smoothingeffect on air waves transmitted therethrough, but thinness of this spaceshould not be carried to the point of throttling the pressuresufficiently to impose a substantial load on the front diaphragm.

It will be evident that having the rear casing and operative mechanismtherein. practically aperiodic as concerns desirable horn frequencies,is of advantage as concerns the front diaphragm. For instance, for astandardized horn, the variation or tolerance permissible for naturalfrequencies of different diaphragms of the same lot is considerable,thus cheapening manufacture. Furthermore, the same casing and operatingmechanism may be standard for horns having diaphragms of widely varyingfrequencies and constructed so as to give notes of desired degrees ofharshness. One feature of the inven-- tion is providing a diaphragmhaving an armature rigidly secured to the diaphragm at its center, buthaving an overhang sufficient to bring its peripheral edge in contactwith the diaphragm when the diaphragm reaches the end of its outwardswing. Such an armature may be of relatively great area to bridge thepoles of a magnet of great diameter and yet have all but the extremecentral portion of the diaphragm free for easy elastic bending.

In this connection, it is to be noted that a iaphragm having such alarge armature closely confronting such a large magnet area operates onthe air within the casing in an entirely different manner from theoperation of the outer surface of that diaphragm, which operates on theatmosphere. On the outside, all of the work goes directly into producingthe useful signal wave, whereas in the casing a large part of the workis done by the rear face of the armature which acts somewhat like apush-pull pump desirable form for the coupling rod shown in Fig. 1;

Fig. 3 is a perspective view of the magnet shell and bracket shown inFig. 1: Figs. 4 and 5 are detail sectional views showing diaphragm andarmature arrangements;

Fig. 6 is like Fig. l, but showing a modified arrangement of reardiaphragm and microphone; while Figs. 7 and 8 are sectional detail viewsshowing make and break contacts that may be used in place of the mcrophone in a structure like Fig. 1.

In these drawings, the horn is shown as coml5 prising a cylindricalcasing I, closed practically air-tight at the enlarged forward end bydiaphragm 2 and at the rear end by smaller diaphragm 3. The frontdiaphragm is securely clamped in position by front casing '4 carrying 20projector 5 through which the sound waves are projected into the air,and the rear diaphragm is secured by rear casing G, which is incommunication with the air through an opening I. This opening is of suchsmall size and is so located that air waves from the projector havenegligib e effect in producing pressures on the rear face of diaphragm3. One advantage of the apparatus is that neither diaphragm is subjectedto any violent stress and will operate indefinitely 30 without breakage.Consequently, if desired, the diaphragms may be permanently secured bybending or spinning over the flanges, 4a for the front casing and 6a forthe rear casing. The usual diaphragm gaskets 2a, 3a, may be employed tospace the diaphragms away from the adjacent metal surfaces, and thesegaskets may be metal, paper, cork, or the like, as may be desired.Obviously, screws may be employed in place of flanges for clamping thediaphragm at the front 40 and rear ends of the casing. The reardiaphragm is of much less diameter and may be of greatest thickness inorder that its rate of elastic return to normal will be much higher thanthat of the front diaphragm. The diaphragms 45 are preferably of finequality spring steel.

Within the casing is secured by rivets 8, the anchorage cross-bar 9,carrying the peripheral pole pieces l0, preferably integral therewith,as shown in Fig. 3, and the central pole piece 50 These field pieces areof soft iron and the central pole may be laminated. It is secured byriveting, as shown in Fig. l.

The energizing coil l2 encircles central pole piece I fitting between itand the shell poles I0. 55 The front diaphragm has a relatively massivelarge-area armature I3, secured to its center as by a rivet M. As shownin Fig. 1, there are intervening washers as, for instance, a large-areawasher l5, between the armature and the rear 60 face of the diaphragmand washers I6, ll between the diaphragm and the rivet head. It will beunderstood that a large area washer l5, on the rear of the diaphragmwill have the effect of filling a much larger central portion of the 65diaphragm for the forward swing than will washers H5 and H, for the rearswing. Consequently, many variations of note quality may be produced byvarying the area and thicknesses of these washers. In addition to this,specially harsh ef- 7O fects may be produced by having the washer be- Iing and insulated therefrom as shown.

' casing and electrode,23 carried by and movable with the diaphragm 2!.These electrodes also 10 may be of phosphor-bronze.

While any desired form of microphonic contact for these electrodes maybe employed, I prefer a simple construction consisting merely ofregistering shallow concavities in the face of electrodes 22 and. 23,each containing a carbon ball 24, said balls being of smaller curvaturethan the cavities but of sufficient diameter to keep the electrodes fromcontact with each other. The rear electrode has a rigid, preferablyintegral shank-25 extending through the rear of the cas- Shank 25 ispreferably utilized to secure the casing in position and at the sametime form a circuit connection for the fixed electrode, as by rivetingsaid 25 shank through a plate 26 of insulating material secured to thebridgel! by screws 21 and formed with a cavity in which the riveted headof 25 is housed, free from contact with themagnet pole piece 3G Thefront electrode 23 also has a rigid, preferably integral extension 29,whereby it is secured.

to the diaphragm 2| of the microphone casing as by clamping nut 30. Thisshank 29 is screwthreaded to form part of an adjustable coupling betweenthe microphone diaphragm 2| and the rear diaphragm 3, thepreferredarrangement being that shown on a large scale in Fig. 2. Herethe microphone electrode shank 29 is screwed'into an internally threadedhead 3|, which has a 40 shank 32 extending through diaphragm 3 butinsulated therefrom by washers 33, 34. The head 3| is clamped in placeby nut 35 and jam nut 36.

As before explained, the purpose of this screw upling to apply suitablepressure on electrode 45, 23 by rearwardly flexing diaphragm 3 therequired distance.

The design is such that in operation developmerit of rearward pressureon the rear dia-v phragm 3 will first operate to relieve the elasticpressure of said diaphragm on said electrode 23 without substantialmotion of the center of said diaphragm 3. Thereafter, further rearwardmovement of diaphragm 3'will positively retract electrode 23. Subsequentdecreasing rearward pressure on 3 will cause reverse operation and thepressure on electrode 23 will be accentuated when a vacuum conditiontends to suck 3 rearwardly. While the apparatus will operate more .orless satisfactor ly with the coupling 29, 3|, of

rigidly fixed length, an important improvement results where there is alost motion interval between the time of thrust of diaphragm 3 onelectrode 23 and the time of retraction by diaphragm 3. As shown in Fig.2, this lost motion may be provided merely by mak ng the threads of 29and 39 a loose fit, in the direction of tension and thrust. With sucharrangement, the normal thrust condition will bring the threads intobearing as indicated at 49 and, as diaphragm 3 moves 7 to the left andthe pressure is released, the diaphragm 3 will continue to moverearwardly for a substantial interval before the other faces 43, of saidthreads, come into contact so that further retracting movement ofdiaphragm 3 will 15 take effect as a retracting tension on electrode 23.A lost motion connection of somewhat similar effect, but by elasticdevelopment, may be had by making the insulating washers 3d of elasticmaterial. It will be noted that in Fig. 1, the distance between frontand rear diaphragm is 2% inches and as previously explained, this is thequarter wave length for 1200 frequency; hence only a fraction of aquarter wave length for 400 to 750 frequency of swing of the frontdiaphragm 2. Consequently, the above described satisfactory pressurecondition will be established in the horn cavity during the rearwardswing of diaphragm 2 and a corresponding vacuum condition will beproduced on the forward swing of said diaphragm. An important point isthat the pressure phase on 3 will lag substantially behind generationthereof by diaphragm 2, and much further lag in final retraction ofelectrode 23 will result from the lost motion connection at 40, 43, withthe composite result that the times of maximum pull and release by theelectromagnet will be in proper phase for efiiciently building up wideswings of diaphragm 2. An important contributing factor is that duringthe lost motion period, when the rear diaphragm 3 is exercising neitherpressure nor tension on electrode 23, said electrode will be held firmlypressed forward by the internal pressure which is then taking effect onthe rearwardly presented surface of the microphone diaphragm 2i. Minuspressure will cause the reverse effect, namely, relief of the microphonepressure during the lost motion part of the elastic return of reardiaphragm 3.

While it is obvious that the 2 inch distance between diaphragms could besomewhat decreased without changing the structure shown in Fig. 1, thereare other designs whereby this distance may be still further decreased,as, for instance, that shown in Fig. 6. In this figure, elements such ascasing members I, 4, 5; diaphragms 2, 3; clamping members 2a, 4a, 3a,6a; electro-magnet elements, 8, 9, In, H, l2; armature I3; etc., may bethe same as in Fig. 1, but

the distance between diaphragms is greatly reduced, by locating themicrophone in the rear of the rear diaphragm; and modifying thestructure of the microphone and linkage so that rearward movement of therear diaphragm will release the pressure on the movable member of themicrophone. Some of these differences are as follows:

The microphone, instead of being mounted on the electromagnet bracket 9,is mounted on the hack of the rear casing member 80, which is providedwith an insulating plate 26a corresponding to 26 of Fig. 1. The fixedelectrode 22a is made in the form of an annulus so that the movableelectrode 23a, mounted on diaphragm 2i may be actuated through thebushing 25b, whereby the fixed electrode 22a, and themicrophone casingare secured to the rear casing 60. The link between rear diaphragm 3 isafforded by a screw member 29a fixed to said diaphragm, preferablynon-adjustably, as by riveting. This screw member engages an internallythreaded screw mem ber Sta which corresponds to SI, Fig. 1, having ascrew threaded shank 32a, whereby the screw coupling between 29a and ammay be adjusted to predetermine the initial tension of rear dia phragm3. In this case, this screw coupling may have lost motion provision asin Fig. 2, for the same purposes and with the same results.

In Fig. 6. the current enters through binding post a, traverses the coil12 serially and is led to 29a, when the current flows through am to 23,thence through 'microphone balls 24 to fixed electrode 22a and cutthrough connection 2, to the other binding post Z7. This corresponds tothe arrangement shown in Fig. l, where the current passes from bindingpost a through the coil and to the shank 25 of the fixed electrode 22,thence through balls 26 to movable electrode 23a, microphone diaphragm2i, microphone casing 20 v and out to binding post I).

There is a feature of the diaphragm and its armature peculiarly adaptingit for the double purpose of efiicient operation as a motor and alsovarying the quality of the note produced. Referring to Figs. 4 and 5,for instance, it will be noted that the front clamping washer l! is ofsmall diameter as compared with the rear clamping washer i511.Consequently, at the front end of the forward swing, the clamping washer[5a renders the diaphragm quite stiff and therefore of relatively shortand swift elastic movements as compared with the corresponding effect ofwasher ll during the rear swing from normal to point of nearest approachto the electromagnet. The point is that the free elastic area of thediaphragm is thus rendered much greater during the part of the swingthat is nearest the electromagnet than it is during the part of theswing more remote therefrom. The slow easy movement adjacent the face ofthe electrom'agnet permits the latter to act a longer time and moreeffectively on the armature when it is nearest the magnet poles.

At the same time, the swift short movement of the diaphragm forward ofnormal generates a 3 higher, shorter time period impulse than does thelonger slower swing to the rear side of normal, thereby producing adouble note effect although the swing of the diaphragm that creates itis, mechanically considered, a true bodily swing on both sides ofnormal. I suppose that the comparatively great flexibility and decreasedresilience of the diaphragm while in the region of the electromagnet isa substantial factor in causing proper in-phase cooperation of thebodily swings with the air-actuated, microphone control fluctuations ofthe current in the electromagnet. However, this may be, there is nodoubt about the great advantages due to the dissimilar effecm of smallfront clamping washers as compared break, in which there is a lostmotion connection between rear diaphragm 3 and the contacts 23!), 3th.The lost motion is provided by having the movable contact carried byspring 50, which is loosely engaged between abutments 5!, 52 on a member53 rigidly but adjustably secured to the center of the rear diaphragm 3.

In this case, the self closing of the contacts during lost motionintervals is by normal elastic bias of spring 56. i

In the foregoing, I have not discussed how the ter, half, three-quarteror full wave length; or

multiples of any of them, for the simple reason that it is uncommercialto make "the casing longer or largerthanit needto befparticularly' wheremy invention makes: phenomenal simplification and efficiency attainablewith the short casing. "It

. will be evident, however, that to whatever extent longer casingsmaybeusable, each and all'of the other above described] combinations; 's'ubcombi 3 nationsland' details of my'invention may b fully employed.1019411111, a 1. -A signaling device, including a tubular member, closedby an acousticdiaphragm' offlsheet steel rigidly clamped about its(peripheryjand with its outer face exposed to atmosphereflandits innerface carrying an armature; and byfam casing member by operation of theacoust v phragm; and an electromagnet arrang tween the diaphragms,inoperative relation to said armat'ur'ej'and in ,combinationwith jallfofdiasaid parts a microphone cell having" another diaphragm, andf a"direct fmlechani'cal conn'ection through whichitis controlled bymovements of said rear diaphragnrtoj. energize said 'f electromagnet,during 1 rearward swing of the ber, closed by anacoustic diaphragmfofsheet steel j'rigidly clamried'j'aboutits periphery and with its outerface exposed to atinos'phere fand its inner face'car'ryinga'n'armature'; fand'by an- 3 v I other elastic diaphragm'exposed' to andactuated acoustic "diaphragm andtode energize it during itsrdrwareswing. x

member by operation of the acoustic diaphragm;

and an electromagnet arranged between the diaphragms, in operativerelation to said armature; and in combination with all of said parts amicrophone cell having another diaphragm, and a direct mechanicalconnection through which it is controlled by movements of said reardiaphragm to energize said electromagnet during rearward swing of theacoustic diaphragm and to release it during its forward swing; saidcontrol being through a connection affording independent or lost motionbetween said rear diaphragm and the microphone diaphragm.

3. A signaling device, including a tubular member, closed by an acousticdiaphragm of sheet steel rigidly clamped about its periphery and withits outer face exposed to atmosphere and its inner face carrying anarmature; and by another elastic diaphragm exposed to and actuated byvarying pressures set up within said casing member by operation of theacoustic diaphragm; and an electromagnet arranged between thediadiaphragms, in operative relation to said armature; and incombination with all of said parts a microphone cell having anotherdiaphragm, and a direct mechanical connection through which it iscontrolled by movements of said rear diaphragm to energize saidelectromagnet during rearward swing of the acoustic diaphragm and torelease it during its forward swing,. said control being through aconnection affording lost motion between said rear diaphragm and themicrophone during a portion of the rearward and forward movements ofsaid rear diaphragm.

4. A signaling device, including a tubular member, closed by an acousticdiaphragm of sheet steel rigidly clamped about its periphery and withits outer face exposed to atmosphere and its inner face c rrying anarmature; and by another t caust diaphragm and to release it duringits"forward elastic diaphragm exposed to and actuated by "varyingpressures setup within said casing member by'operjationof the acoustic:diaphragm; and 'an electromagnet arranged" between the I dia-"-phra'grnsjinoperative relation to said armature;

and in combination'with all of said parts a microphone-cellhavingf'another"diaphragm, and a direct rnechanicalfconnection"through" which it is. controlled by'moveme'nts of'saidrear diaphragmto-eiiergise"saidelectromagnet during rearward swing"of{the*acoustic-diaphragm and to release 'lts' forward s'wingysaid control beingthrough a connection =aifordinglost'motion"between said rear diaphragmand the 'mic'r'oph'one" during" an "early portion-off the rearwardmovement and a "late"'port'ion or the'forw'ardmovement'oi said'rear 5otherelastic diaphragm jexposed'toja'ndactu'atdi p "ed by varyingpressures 'set""upj within said a tubular niembenfclosed by-an'acoustio'diaphragm offsheet' steef rigidly clamped about its "peripheryand with its outer face exposed to at-; mosphere -"and its innerface-carrying anarmature-yand-by'another elastic diaphragm actuated Asignaling device, including in combination by and-in"accordancewithvaryingp'ressures set up within said casing member byoperation of theacoustic" diaphragm-g and an electromagnetarrange'd between thediaphragms in operative relation to said armature; the distance betweensaid diaphragms being less-than a quarter length "*of a'souncl-wavecorresponding to the period'of free elastic vibration -of' said acousticdiaphragm, "in combination with a: microphone controlled bymovementsfofsaid rear diaphragm to energize said electromagnet during:rearward swing of the 6; A signaling device, including-in combination atubular member, closed by an acoustic diaphragm of sheet steel rigidlyclamped about its periphery and with its outer face exposed toatmosphere and its inner face carrying an armature;'and by anotherelastic diaphragm exposed to and actuated by varying pressures set upwithin said casing member by operation of the acoustic diaphragm; and anelectromagnet arranged between the diaphragms, in operative relation tosaid armature; the distance between said diaphragnis being less than aquarter length of a sound wave corresponding to the period of freeelastic vibration of said acoustic diaphragm, in combination with amicrophone controlled by movements of said rear diaphragm to energizesaid electromagnet during rearward swing of the acoustic diaphragm andto release it during its forward swing, said control being through aconnection affording independent or lost motion between said reardiaphragm and the microphone.

'7. A signaling device including a casing, an elastic main diaphragm ofsheet steel rigidly clamped about its periphery and having its frontface exposed to atmosphere and its rear face closed in by a casing, amovable member of electromagnetic material, secured to the rear face ofthe main diaphragm and an electromagnet adapted to attract said movablemember to retract said diaphragm and then release the same, saidelectromagnet being rigidly mounted in spaced relation to the walls ofthe casing so as to afford free peripheral space enclosing an air columnfor propagation of waves from the rear face of the main diaphragm to therear of said casing, and in combination with all of said parts anotherelastic diaphragm having one face only exposed to the varying pressuresset up in said casing by said main diaphragm, a circuit controllerforvariably energizing said electromagnet, and connecting means betweenthe latter diaphragmand the circuit controller, for actuating thecontroller to energize the magnet in step with the bodily swings of themain diaphragm.

B. A signaling device including an elastic main diaphragm of sheet steelrigidly clamped about its periphery and having its front face exposed toatmosphere and its rear face closed in by a casing, a movable member ofelectromagnetic material, secured to the rear face of the main diaphragmand an electromagnet adapted to attract said movable member to retractsaid diaphragm and then release the same, and in combination with all ofsaid parts another elastic diaphragm having oneface only exposed to thevarying pressures set. up in said casing by said main diaphragm, acircuit controller for variably energizing said electromagnet, andlostmotion connecting means between the latter diaphragm and the circuitcontroller, for actuating the controller to energize the magnet in stepwith the bodily swings of the main diaphragm.

9. A signaling device including a main diaphragm of spring metal, anarmature carried by said diaphragm, a casing member and means forrigidly clamping the diaphragm about its periphery to form a closedfront end for said casing, an electromagnet supported in the casing forintermittently attracting said armature and actuating said diaphragmand, in combination with all said parts, means for intermittentlyenergizing said electromagnet in step with the natural elastic swing ofsaid diaphragm as determined by elasticity and inertia of said diaphragmand armature; said' means including a secondary diaphragm in the rear ofthe electromagnet with its face exposed to and actuated by changes ofpressure within the casing due to the bodily swings of said maindiaphragm, means for limiting vibratory movements of said secondarydiaphragm so as to prevent resonant vibration thereof, a microphone forcontrolling flow of current through the electromagnet and means fortransmitting motion of said secondary diaphragm to said microphone.

1 0.1.A'signaling device including a. main diaphragm of spring metal, anarmature carried by said diaphragm, a casing member and means forrigidly clamping the diaphragm about its periphery to form a closedfront end for said casing, an electromagnet supported in the casing forintermittently attracting said armature and non-positively actuatingsaid diaphragm and, in combination with all said parts, means forintermittently energizing said electromagnet in step with the naturalelastic swing of said diaphragm as determined by elasticity and inertiaof said diaphragm and armature; said means including a secondarydiaphragm in the rear of the electromagnet with its face exposed to andactuated by changes of pressure within the casing due to thebodily-swings of said main diaphragm, means for limiting vibratorymovements of said secondary diaphragm so as to prevent resonantvibration thereof, a microphone for controlling flow of current throughthe electromagnet, and a lost motion linkage through which the movementsof the secondary diaphragm, are applied to vary the resistance of themicrophone.

. JOHN F. MORAN.

